1. Field of the Invention
The present invention relates to an image-processing apparatus, an image-processing method and a recording medium, and relates to, for example, image processing performed to control the amount of applied coloring materials.
2. Description of the Related Art
There have been increasing occasions where data which was generated by a personal computer (PC) or the like was printed through an image-processing apparatus having a printing function. The image-processing apparatus including a laser-beam printer or the like receives data on a command relating to printing, data on encoded characters, and drawing information that are transmitted from a host computer including the PC, a work station, etc. The image-processing apparatus converts the received command data into pixel-information items through a rendering unit and forms an image based on image signals generated based on the pixel-information items.
More specifically, first, a photosensitive drum is uniformly charged by using a charge roller or the like, and an electrostatic-latent image is formed on the photosensitive drum by using the image signal generated based on the above-described pixel-information items, for example, by exposing the photosensitive drum to laser light emitted from a laser scanner. The above-described formed electrostatic-latent image is developed by a developing device and a developed toner image is transferred to a transfer material through a transfer roller or the like. Then, the toner image is permanently fixed on the transfer material through a fixing device so that the image is printed.
On the other hand, when the amount of toner adhered during the development is large, that is to say, when the amount of applied toner is large, the toner is not thoroughly fixed but scattered. Further, the toner comes off a part where the dot density is high. The frequency of occurrence of the above-described problems varies with environmental circumstances surrounding the image-processing apparatus, the environmental circumstances relating to humidity, temperature, etc. Here, there are many types of mediums used for printing, such as paper. However, problems similar to the above-described problems often occur depending on the types of mediums.
Further, when a line image 102 is printed in a main-scanning direction, toner is scattered to the rear of the line image 102 in a sub-scanning direction so that the image is disturbed, the line image 102 being recorded onto a transfer material 101, as shown in FIG. 1. FIG. 2 shows the reason for the above-described problem. Namely, since a sudden rise in temperature occurs when the transfer material 101 passes through a fixing device 201, water vapors 202 are generated from the moisture content of the transfer material 101. At that time, the water vapors 202 of the transfer material 101 on which a large amount of toner 203 is applied cannot escape so that the toner 203 is blown off by the water vapors 202 to the rear in a conveying direction. From now on, the above-described phenomenon where toner is scattered in the sub-scanning direction toward the rear of a linear image extending in the main-scanning direction so that the line image is disturbed is referred to as a tailing phenomenon.
Methods of reducing the amount of adhered toner have been used, so as to reduce the above-described tailing phenomenon. More specifically, in general, a method of reducing the development ability, namely, a method of reducing the direct-current component of a developing bias and/or a method of thinning out dot data of image data for which image formation is performed has been used (refer to Japanese Patent Laid-Open No. 2000-175029 and Japanese Patent Laid-Open No. 2001-80112, for example). When the development ability is reduced by changing the developing bias, the adhered-toner amount is decreased so that the problems including toner scattered around characters, toner tailing, etc. are reduced. However, since the amount of toner applied on the edge part of image data is significantly decreased, the image quality is decreased. Further, the density stability is decreased when being put through an endurance test.
Further, reducing the dot data by performing the thinning-out processing for the image data has been perceived as processing decreasing the image quality. Particularly, when the thinning-out ratio is increased until the tailing phenomenon disappears completely, image deterioration occurs, as a decreased line width, a reduced density, omission of image data, etc. depending on the degree of the tailing phenomenon, even though the degree of the tailing phenomenon varies with the environmental circumstances and the medium types.
Japanese Patent Laid-Open No. 2005-70432 discloses the technology of performing the thinning-out processing, so as to reduce the tailing phenomenon while decreasing the image deterioration. According to Japanese Patent Laid-Open No. 2005-70432, a predetermined image pattern is extracted, the thinning-out processing is performed for the area of the extracted image pattern, and line data is added to the upper-most part and/or the lower-most part of the extracted image pattern. According to Japanese Patent Laid-Open No. 2005-70432, image data is added, as an attempt to prevent image deterioration including a reduced line width, a reduced density, etc.
According to the above-described known methods, however, as the laser-light amount, the manner in which a drum functions, using circumstances, etc. vary with image-processing apparatuses, image-forming conditions vary with the image-processing apparatuses. Therefore, when the line data is added to the image data, the most appropriate number of lines for addition varies with the image-processing apparatuses, so that in reality it is difficult to perform control relating to determination of the amount of data to be thinned out and the number of lines for addition.
Further, when data on images such as three or four line images is added to the image data, so as to achieve the density conservation, the image data is thickened, which makes it difficult to correctly reproduce an original image.